1. Field of the Invention
The present invention concerns a technique to determine the classification of sheets used in image forming apparatus.
2. Description of the Related Art
In recent years, with a view toward environmental problems and recycling of resources, workplaces using large quantities of paper in copying machines and printers and the like have begun reusing sheets of paper ordinarily used for forming images on only one side of them by forming images on the blank side of them on the opposite side of which images have already been recorded (hereafter, “reversed sheets”).
Because the reversed sheets are increasingly being used in image forming apparatus, inventions that address the use of the reversed sheets have appeared, for example inventions that improve the efficiency of use of reversed sheets (for example, see Japanese Patent Application Laid-Open Publication 2001-235906, hereinafter, JP 2001-235906).
The image forming apparatus disclosed in JP 2001-235906 is equipped with a storage part for blank paper that stores unused paper and with a reversed sheet storage part that stores reversed sheets. When a sensor in this image forming apparatus detects paper in the reversed sheet storage part, the user selects whether to form images on unused sheets or on reversed sheets, and if the use of reversed sheets is selected, the apparatus forms images on the paper stored in the reversed sheet storage part.
For an image forming apparatus that forms images using an electrophotography system, heat and pressure are applied to the paper for the purpose of fixing the image; however, the absorbed moisture in unused paper evaporates, and the paper lengthens. As well, for image forming apparatus based on inkjet systems, swelling of the paper occurs because of absorption of ink in the spaces between the fibers of the paper (capillarity), and this causes the paper to lengthen, in much the same way that paper is lengthened by fixing. For this reason, it is desirable to form images on unused paper taking such lengthening into account, and for reversed sheets, because this lengthening has already arisen due to fixing, it is desirable to form images taking into account the absence of lengthening.
For the image forming apparatus disclosed in JP 2001-235906, in the case where paper is provided from the reversed sheet storage part, because the stored paper is reversed sheets, it is desirable not to correct the images. However, for the image forming apparatus disclosed in JP 2001-235906, because the configuration of each storage part is identical, there is the problem that the user might confuse unused sheets and reversed sheets and store the wrong paper by mistake. If the user confuses the storage of unused sheets and reversed sheets, and image corrections for unused paper will end up being done on reversed sheets, giving rise to the problem that the image formed will differ from the intended image.